DIAMOND: OCCURRENCE IN SOUTH AFRICA 193 



It is found in the form of rounded or angular grains, crystals, or even indications of 

 crystalline form, being never observed. The grains are usually in a fresh and unaltered 

 state, and therefore appear bright and transparent, some, however, are cloudy and opaque, 

 and of a reddish-brown colour, in consequence of a process of decomposition having 

 commenced. The colour of the unaltered garnets is variable, a deep wine- or hyacinth-red 

 is most frequent, red tinged with violet is less common, while light or dark brownish-yellow, 

 and a beautiful ruby-red are colours which are seen but rarely. Garnets of this ruby-red 

 colour are cut for gems and enter the market under the name of " Cape rubies." In size 

 the garnet grains vary from mere dust up to the size of a walnut. All specimens yet 

 examined contain a little chromium, and have the chemical composition of pyrope, itself 

 well known and much used in jewellery under the name Bohemian garnet. 



The members of the pyroxene group most frequently met with are enstatite (and 

 bronzite) and chrome-diopside. The enstatite has the usual composition, but not the 

 usual appearance of this mineral. It occurs generally in fragments about the size of a 

 hazel-nut. It is transparent, with the colour of green bottle-glass, and has a distinct 

 cleavage and a conchoidal fracture. It closely resembles olivine in appearance, and is 

 frequently confused with this mineral. It is often found intergrown with garnet in such 

 a way that single grains of gamet are enclosed by a shell of enstatite. This variety of 

 enstatite is of more common occurrence than is the garnet. Another variety of enstatite 

 (bronzite) also occurs, but more rarely. It is brown in colour and less unlike the ordinary 

 mineral in appearance ; moreover, it has a distinct plane of separation in one direction. 



Chrome-diopside, sometimes referred to as chromiferous diallage, though less common 

 than garnet, is yet very frequently met with. It occurs in irregular polyhedral grains of 

 about the same size as the garnet grains and with no trace of crystal-faces. It is emerald- 

 green in colour, translucent in mass, but transparent in thin splinters, and is usually 

 distinctly cleavable in one direction. WoUastonite, another mineral of the pyroxene group, 

 is also said to occur in the '' blue ground." 



The amphibole group of minerals is represented by the green smaragdite, which, 

 however, is of rare occurrence. It has possibly been derived by the alteration of chrome- 

 diopside. The occurrence of treraolite and asbestos has also been reported. 



An altered magnesium mica occurs everywhere in small shining scales of a greenish 

 or brownish colour or completely bleached. These thin plates or prisms frequently have 

 a regular six-sided outline, and show the characteristic cleavage of mica ; optically they are 

 almost uniaxial. This altered mica, which is distinguished as vaalite, sometimes occurs 

 aggregated into brown balls the size of a hen's egg, and in some places forms the chief 

 constituent of the " blue ground." The glittering scales of mica embedded in the " blue 

 ground " are sometimes mistaken at first sight by the unpractised eye for diamonds. 



Ilmenite (titanic iron ore) is another mineral frequently associated here with the 

 diamond. It occurs in shining black rounded grains with no indication of crystal-faces. 

 It contains some magnesia and is not magnetic. Formerly the diamond miners imagined 

 this mineral to be the black variety of diamond known as carbonado, and at present found 

 almost exclusively in Brazil. They were not easily convinced of their error, and the name 

 they gave it, carbonado, still remains. True carbonado occurs only very sparingly at the 

 Cape. Magnetite (magnetic iron ore) in grains and of the usual character is said to be of 

 frequent occurrence. Chromite (chromic iron ore), found in brilliant shining black grains 

 up to the size of a pea, and with a conchoidal fracture, is also fairly common. Zircon, 

 known to the Kimberley miners as "Dutch bort," occurs very rarely in transparent to 

 translucent grains of a very pale flesh colour, and about the size of a lentil or pea. Other 



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